Re: [PATCH 2/7] block: Remove bio->bi_ioc

[Ming Lei <ming.lei@redhat.com>]

On Tue, Nov 20, 2018 at 11:58:09PM +0000, Damien Le Moal wrote:
> On 2018/11/21 2:31, Jens Axboe wrote:
> > I think the below should fix it, we haven't necessarily setup an
> > ioc if we're just doing as passthrough request.
> > 
> > 
> > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> > index 13b8dc332541..f096d8989773 100644
> > --- a/block/blk-mq-sched.c
> > +++ b/block/blk-mq-sched.c
> > @@ -34,9 +34,16 @@ EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
> >  void blk_mq_sched_assign_ioc(struct request *rq)
> >  {
> >  	struct request_queue *q = rq->q;
> > -	struct io_context *ioc = current->io_context;
> > +	struct io_context *ioc;
> >  	struct io_cq *icq;
> >  
> > +	/*
> > +	 * May not have an IO context if it's a passthrough request
> > +	 */
> > +	ioc = current->io_context;
> > +	if (!ioc)
> > +		return;
> > +
> >  	spin_lock_irq(&q->queue_lock);
> >  	icq = ioc_lookup_icq(ioc, q);
> >  	spin_unlock_irq(&q->queue_lock);
> 
> This seems reasonable to me, but I wonder why this problem was not triggering
> before. The previous code getting the ioc with the rq_ioc(bio) call was
> essentially the same and there was no "if (!ioc) return;" in
> blk_mq_sched_assign_ioc() before the patch.
> Any idea why this is popping up now ?
> 
> Ming,
> 
> Is this a new test your are running ? If this same problem triggers on stable
> kernels, Jens patch needs to go to stable too.

No, I run daily block related tests on block for-next, and this issue is
just triggered when your patches landed.

You may find the test script:

https://people.redhat.com/minlei/tests/tools/elv-switch

Thanks,
Ming